Recently, the revolution per minute (RPM) of a spindle motor in a disk driver has been continuously increased due to the increase of information-recording density of the data storage disk. However, problems regarding the high-speed spin of the data storage disk have been exposed, for example, the increase in breakage of the disk during operation, and most seriously, injuries caused by cracked disks flying out of the disk driver. Therefore, to design a disk capable of limiting breakage is the focus of development in the industry.
FIG. 1 illustrates a conventional disk. It is known by those skilled in the art that when the disk spins at a high speed, the disk has a highest stress in the inner edge 103. Therefore, a crack is generally generated on the inner edge and advances to the outer edge 101.
When the crack generated in the disk reaches the critical crack length, the advance of the crack increases substantially to make the disk break. It is also known that as the spin speed increases the critical crack length decreases.
The commercial high-speed disk driver generally has a speed of 48×or 52×. According to David Nowell's experiments and theory, when the speed is 48×, the critical crack length is about 1.72 cm; when calculating by the destructive mechanics, the theoretical critical crack length becomes about 0.83 cm, which is about one half of the experimental value. When the speed is 52×, the experimental critical crack length is about 1.25 cm, and the theoretical critical crack length is about 0.6 cm, which is about one half of the experimental value. The factors of differences between experimental and theoretical values have been discussed in David Nowell's article and will not be elaborated herein.
Therefore, there is a need to provide a disk suitable for operating at a high spin speed and capable of hindering a crack from advancing over the experimental critical crack length.